This work aimed the synthesis and characterization of eight cobalt(II) complexes which could be able to act as controlling agents in vinyl acetate radical polymerization mediated by cobalt. By modulating the coordination sphere of these complexes, modifying the steric and electronic effects offered by the α-diimine ligands, we sought to establish parameters to propose how these complexes mediate the CMRP of vinyl acetate. The complexes were split in two groups in way to assess efficiently how the electronic and steric effects can affect the controlling capacity of the CoII(α-diimine).A systematic variation of the molar ratio such as [Co]/[initiator] and [Co]/[monomer] made it possible to choose [Co]/[initiator]/[monomer] = 1/3.25/542 as the ratio that provided certain level of control. The addition of DMSO was detrimental to the complexes 2a-c, but caused an improvement to the activity of complexes 2dh, reducing their polydispersity values and increasing the molecular weights of the polymers. Complex 2b was chosen as the best controller of the steric effect group, its steric and electronic characteristics made possible to reach the lowest polydispersity of its group (Đmax = 1.43).Regarding to the group of complexes of the electronic effect, it was the complex 2f that had the smallest polydispersity of its group, between 1.12 and 1.58, due to the greater structural stability conferred to the complex by its cyclohexyl substituent.